Gas operated seismic source employing an inflatable member

ABSTRACT

A gas operated seismic source has a rigid elongated cylindrical form and includes at least a single, hollow, thick wall barrel along most of the central length thereof, wherein the internal volume defines therein a combustion chamber. The barrel has a plurality of perforations formed along its length of a selected number, size or sizes, and arrangement. An inflatable member is secured at either end thereof about the perforated barrel to enclose the perforations and define accordingly an expandable outer wall about the combustion chamber. The perforated barrel has a substantially constant diameter as does the inflatable member, and the barrel supports the inflatable member when in its collapsed state. Thus the outside dimensions of the entire length of the source are substantially constant to allow the source to be readily forced or &#39;&#39;&#39;&#39;planted&#39;&#39;&#39;&#39; into and also retrieved from a consolidated or an unconsolidated formation, or to readily allow inserting the source into a predrilled hole in a consolidated formation. Means are provided to introduce a preselected mixture of combustible fuel into the combustion chamber. Upon firing, the burned gases are forced out an exhaust means by the explosion and the subsequent charge of combustible fuel, or the combustion chamber is purged by employing vacuum or pressure.

United States Patent Knight et al.

Oct. 24, 1972 [72] Inventors: Paul A. Knight; James R. Saunders; Fred E. Stapleton, all of Houston, Tex.

['73] Assignee: Mandrel Industries, Inc., Houston,

Tex.

[22] Filed: Feb. 27, 1970 [21] Appl. No.: 14,923

[52] US. Cl. ..l81/.5 NC, 340/5, 340/15 [51] Int. Cl. ..G0lv 1/14 [58] Field of Search...l8l/.5 AG, .5 H, .5 NC; 340/5, 340/ 12, 15

[56] References Cited UNITED STATES PATENTS 3,380,551 4/1968 Lang ..181/.51C 3,478,838 11/1969 Kilmer ..l8l/.51C 3,480,101 11/1969 Barry et al. ..l8l/.51C 3,176,787 4/1965 Roever ..l81/.5l C 3,379,273 4/1968 Chelminski ..18l/.5 H 3,525,416 8/1976 Mott-Smith ..18l/.5 H 3,187,831 6/1965 Smith, Jr. ..l8l/.5 NC

Primary Examiner-Benjamin A. Borchelt Assistant Examiner-N. Moskowitz Att0rney-Robert G. Clay [57] ABSTRACT A gas operated seismic source has a rigid elongated cylindrical form and includes at least a single, hollow, thick wall barrel along most of the central length thereof, wherein the internal volume defines therein a combustion chamber. The barrel has a plurality of perforations formed along its length of a selected number, size or sizes, and arrangement. An inflatable member is secured at either end thereof about the perforated barrel to enclose the perforations and define accordingly an expandable outer wall about the combustion chamber. The perforated barrel has a substantially constant diameter as does the inflatable member, and the barrel supports the inflatable member when in its collapsed state. Thus the outside dimensions of the entire length of the source are substantially constant to allow the source to be readily forced or planted into and also retrieved from a consolidated or an unconsolidated formation, or to readily allow inserting the source into a predrilled hole in a consolidated formation. Means are provided to introduce a preselected mixture of combustible fuel into the combustion chamber. Upon firing, the burned gases are forced out an exhaust means by the explosion and the subsequent charge of combustible fuel, or the combustion chamber is purged by employing vacuum or pressure.

18 Claims, 19 Drawing Figures PUMP 1 7 PATENTED 061 241912 SHEET 1 [If 4 momDow EDL mmmmm INVENTORS PAUL A. KNlGHT, JAMES R. SAUNDERS, FRED E. STAPLETON ATTORNEY :E'IE

PATENTED BT 24 9 2 3. 700.066

saw u or 4 254 252 TII3 lEI 246 250 PAUL A. KNIGHT, JAMES R. SAUNDERS, BY FRED E. STAPLETON mxa ATTORNEY H k INVENTORS TIE IEI GAS OPERATED SEISMIC SOURCE EMPLOYING AN INFLATABLE MEMBER BACKGROUND OF THE INVENTION 1 Field of the Invention The invention relates to seismic sources, and more particularly to a plantable source of substantially constant diameter, having an explosively inflatable member which, upon abrupt inflation provides a relatively large expanding area for efficiently coupling the energy generated by the explosion to the surrounding formation.

2. Description of the Prior Art There are countless types of seismic sources available for conducting seismic surveys on land, or in water covered areas. Various ones of these sources provide some type of inflatable member for imparting the energy generated into the surrounding medium, be it water or land. Typical among the inflatable member type of source are marine seismic sources, which further employ explosives and/or explosive gas mixtures to generate a seismic signal in the water medium. In the latter devices, acetylene, propane, etc, and oxygen are mixed either before or during introduction to a combustion chamber, and are suitably ignited upon mixing by a spark discharge device.

In one type of device the combustion chamber may be a perforated support member of selected shape having an inflatable member secured thereabout and in another type of device the combustion chamber may be formed of the inflatable member itself. In either type of source, the force of the explosion varies the cross section of the inflatable member to increase the volume thereof and introduce a seismic signal into the surrounding medium.

Typical of a source wherein the combustion chamber and inflatable member are one and the same are sources wherein an inflatable member is formed of a generally flat, elongated tube, formed of a pair of flexible walls. The tube provides a non-collapsable minimum volume defining the initial combustion chamber, wherein upon ignition of an explosive mixture, the tube expands to a maximum volume larger than the minimum volume without actually stretching the wall of the tube. In these sources the cross section only is changed to provide the larger volume, (i.e., the tube walls are not stretched). Further such device construction is not conducive to insertion into a predrilled hole in a consolidated formation.

Sources are available wherein the combustion chamber is defined by some form of perforated support member, with the inflatable member secured thereabout. These sources cannot be readily planted in unconsolidated formations and are not readily suitable for insertion into predrilled holes in a consolidated formation due to various apendages thereon or to use of varying cross sections. Further, the devices generally employ complicated annular mixing chambers with separate ignition chambers and also provide for exhaust out the bottom of the devices through continually open exhaust conduits. In some devices exhaust must be out the bottom (i.e., the opposite end with respect to the mixing and firing end) since the device operation is based on providing a desired detonation velocity during the explosion process to provide the seismic pulse. Other devices require a larger variation in cross sec- 0 bustible fuel and a plurality of ports about a circumference thereof. Upon ignition the force of the explosion is rapidly released via the plurality of ports,

whereby coupling is provided from the source to the v soft formation via the conventional bubble theory. Since the efficiency of coupling to a formation is proportional to the area of the formation acted upon by the device, such form of coupling, particularly to an unconsolidated medium, is relatively inefficient.

There are still other devices also particularly designed for marshland seismic surveying. By way of example, typical tyereof are devices which utilize inverted, cupshaped, chambers, etc, which are placed on the soft formation. Means are provided to force the source into the formation while water is pumped away to allow the source to settle firmly into the formation. Seismic signals are generated by integral vibrator means in generally conventional fashion. Such devices are generally bulky and require a prohibitively large array of vacuum pumps, water pumps, vibrating devices and associated valving and electronic control circuits. This latter type of device further is not suitable for use in consolidated formations either at the surface or in predrilled holes.

SUMNIARY OF THE INVENTION The present invention provides a seismic source which is particularly useful in unconsolidated or semiconsolidated areas as well as in land surveys using a predrilled hole. The invention is relatively simple in design, easily handled and operated in the field, and provides relatively efficient coupling of the energy generated by the device to either consolidated, semiconsolidated or unconsolidated formations.

Accordingly, the present invention includes a long thin profile having a substantially constant outside diameter and essentially no obstructions along the outer circumference or end. The gun is rigid and is closed at the bottom end, whereby it may be forced, or planted into an unconsolidated formation or may readily inserted and withdrawn from a predrilled hole in consolidated formations, utilizing suitable mechanical or hydraulic apparatus. The source may also be used in semi-consolidated formations such as in desert areas wherein thick, loose sand formations preclude the use of conventional drilling techniques.

To this end, one embodiment of the invention source includes a relatively thick walled, selectively perforated barrel, extending generally the greatest portion of the source length and generally defining therein a combustion chamber. The barrel is closed at the bottom end thereof with a solid plug, or with a drill bit either of which may have a series of holes drilled therein to form a jetting nozzle for ejecting a selected fluid, e.g., water, air, etc, into the formation. The other end of the barrel is integrally connected to a support member,

which includes therein a plurality of threaded bores for threadably receiving an exhaust valve, a gas fill tube, and if desired a fluid jetting pipe and a shot sensing device. A length of tube may, or may not be, concentrically secured to the support member within the barrel to define therein a difiuser" element. The barrel (as well as the diffuser, if used) is selectively perforated with a predetermined number, size, shape and arrangement of slots, ports or openings. The barrel may also be formed of a circularly spaced plurality of hollow tubes, wherein the perforations are formed by the spacings between succeeding tubes. An inflatable member or bladder is secured, in sealed relation, to the barrel to completely enclose all openings in the barrel. The gas fill tube, and the water jetting pipe (when used), extend through the threaded support member, and into the central region of the combustion chamber defined by the barrel, or the diffuser if used. When employed, the water jetting pipe connects to the series of holes forming the jetting nozzle in the end plug or drill bit. A combustible fuel is introduced into the combustion chamber via the gas fill tube where, upon ignition, explosive energy is generated within the combustion chamber, and is passed via the openings in the diffuser and/or barrel, to abruptly inflate the bladder disposed thereabout. The shock of the sudden inflation imparts a seismic signal into the surrounding medium with optimum energy transfer.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a partially broken-out view of a seismic source in accordance with the invention.

FIG. 2 is a partial cross section of the source of FIG. 1 in greater detail, including details of one embodiment of an exhaust valve.

FIGS. 3, 4 and 5 are cross sections taken along the lines 3-3, 44 and 5-5 respectively of FIG. 2.

FIG. 6 is a cross section of an alternative embodiment of the exhaust valve.

FIGS. 7 and 8 are cross sections taken along the lines 7-7 and 8-8 respectively of FIG. 6.

FIG. 9 is a partially broken-out view of an alternative embodiment of the invention source employing only a perforated barrel, and including an expansion retainer net.

FIGS. 10 and 13 are cross sections of further alternative embodiments of the invention showing a different configuration of perforations in a source with only a barrel, and a source configuration which provides internal cooling means, respectively.

FIGS. 11 and 14 are cross sections taken along lines 1 l and 14 of FIGS. 10 and 13, respectively.

FIG. 12 is a partial section depicting an adapter means for coupling a plurality of sources together.

FIG. 15 is an elevation of a modified drill bit which may be used in place of the end plug shown in the previous embodiments.

FIGS. 16, 17 and 18 are partial sections showing alternative inflatable member configurations, and/or barrel or diffuser perforation configurations, which may be employed in various combinations thereof with the previous embodiments.

FIG. 19 is a partial section depicting yet another embodiment of the invention employing an inflatable member which is open at one end only.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring first to FIG. 1, there is shown an embodiment 10 of the present invention, including a relatively thick wall barrel 12 having an end plug 14 threadably secured at one end thereof, and a support member 16 integrally secured to the other end. The end plug 14 is provided with a series of holes which define jet nozzle means 20. An inflatable member 18, formed for example of a tough but resilient rubber or plastic, entends generally the length of the barrel 12, and is secured at either end thereof to the barrel 12 by suitable fasteners such as hose clamps 22. By way of example only of this specific embodiment, a diffuser tube, hereinafter termed a diffuser 24, is concentrically disposed within the barrel 12, and is rigidly secured to the support member 16 at the respective end thereof. The barrel 12 and the diffuser 24 are selectively perforated with an alternating arrangement of slots and ports along the lengths thereof, as further described below. Exhaust valve means 26 is secured to the opposite (top) end of the support member 16, and in turn is coupled to an exhaust pipe 28 which provides connection to additional pipe (not shown) which leads to the surface of the formation in which the source is planted. Likewise, a gas fill and ignition tube 30 extends along the exhaust pipe 28 into the diffuser 24 to a point generally at the midpoint of the combustion chamber defined therein whereby introduction as well as ignition of the gas occurs preferably at the center of the single combustion chamber. A water or air jetting pipe 32 extends through the diffuser 24 via the support member 16 and is connected at its respective end to the jet nozzle means 20 formed in the end plug 14. A length of the water or air jetting pipe 32 extends along the exhaust pipe 28 and the gas fill and ignition tube 30. A push or drill tube 34, formed of a relatively thick wall, hollow pipe, is threadably attached at its respective end to the support member 16, and has an outer diameter consistent with that of the member 16 and inflatable member 18 when the latter is collapsed. The other end of the push tube 34 is provided with an internally threaded member 36, whereby the push tube 34 and thus the seismic source 10 can be connected to a mechanical or hydraulic apparatus for planting and/or retrieving the source from the formation, e.g., to the drill stem of a modified drilling rig mounted on a suitable vehicle such as, for example, a swamp buggy, etc. When employing the source in predrilled holes in consolidated formations, the device may be extended by using a long (e.g., 15 foot or more) push tube 34, wherein the various pipes 32, 28 and gas fill and ignition tube 30 are attached after the source is in place. Openings 38 are provided in the upper" end of the push tube 34 whereby access is provided to the respective ends of the tube 30 and pipes 32, 28, whereby combustible fuel and water may be introduced to the source, and means is provided to vent the exhausted gases to the surface.

To illustrate that the jetting pipe 32 and the jet nozzle means 20 need not be used, an air or water pump means 29 is herein depicted in phantom line, coupled to the jetting pipe 32. The pump means 29 includes suitable control valve means (not shown) for selectively introducing air or water to the jetting apparatus. A fuel source means 31 for supplying a combustible fuel mixture (e.g., air or oxygen and propane, acetylene,

butane, etc.), is coupled to the gas fill and ignition tube 30 whereby preferably both the gas fill and ignition processes are accomplished, as further described hereinafter. The degree of gas fill is controlled by sensing the gas flow volume or the fill pressure within the combustion chamber of the source which corresponds to the gas flow volume through, or the pressure in, the fill and ignition line 30. Typically, a pressure sensing and feedback means 33 is placed in communication with the line 30 to sense the pressure therein and feed a signal indicative of a preselected pressure back to the fuel source means 31 (indicated at 35) to control operation of the latter. Obviously, the pressure sensing and feedback means 33 may be made an integral part of the fuel source means 31; e.g., may be coupled thereto in the region of the fuel mixing chamber. Vacuum pump means 37 is coupled to the gas fill and ignition line 30 via a valve 39, whereby a vacuum can be drawn in the combustion chamber volume via the line 30 to purge the combustion chamber of burned gases after firing and before recharging the source. The valve 39 opens the line 30 to the vacuum pump means 37 when the latter is in operation, and closes when the vacuum pump means 37 stops after pulling a desired vacuum. An air compressor or pump, such as pump means 29, may be employed in place of the vacuum pump means 37 to supply pressurized air via valve 39 into the combustion chamber volume, to thus purge the burned gases from the source via the exhaust valve means 26.

Referring now to FIGS. 1 and 2, there is shown in greater detail by way of example only, the internal construction of the embodiment of FIG. 1. Accordingly, the barrel 12 comprises a preferably metallic tube of sufficient wall thickness to accept and direct the expanding gases, due to the explosion, outward to the inflatable member 18. The length and diameter of the barrel 12 is chosen commensurate with the selected size of the seismic source; the barrel 12 is sufficient in diameter to permit the diffuser 24 to be concentrically disposed within its length with a radial clearance of the order of, for example, 75 inch between the diffuser and the inside wall of the barrel. The barrel 12 is secured at its upper end to a thick wall cylinder 43 forming the support member 16. (Note that for purposes of description the lower end is hereinafter defined as that end which terminates with the end plug 14, and the upper end is the end through which the various pipes and tubes extend to the surface. However, it is not intended to limit the operation of the invention to such an orientation since the seismic source 10 may be used with any orientation; e.g., vertical, horizontal, etc.). Accordingly, the upper end of the support member 16 includes an externally threaded bulkhead or mounting divider 40 which provides means for securing the exhaust valve means 26, the gas fill and ignition tube 30 and the water jetting pipe 32 if employed, within the upper end of the source. FIG. 5 shows a view of the divider 40 cross section, wherein pipe 32 and tube 30 are spaced and supported by passages drilled in the divider 40. An internally threaded pipe 42 may be provided coupled to the divider 40 which receives an externally threaded end 44 of the exhaust valve means 26. An additional support disc 41 is disposed within the lower end of the support member cylinder 43 and is welded etc, to the end of the barrel 12. The diffuser 24 is secured to the support disc 41, which is provided with holes to allow passage or connection thereto of the various tubes and pipes 30, 32 and 42. The mounting divider 40 may be provided with an internally threaded bore 46, whereby time break switch means 47 (FIG. 9) such as an electromechanical transducer, may be secured to the top of the seismic source 10 to provide a voltage signal at such time as the seismic source is fired, which signal is utilized as a timing reference (e.g., to provide time to) as further described below. Note that the combination of support member 16; viz, disc 41, cylinder 43 and bulkhead or support divider 40, pipes 32, 42 and tube 30, may be replaced or may include a solid cylinder member 43 (not shown) suitably drilled to provide the required passageways therethrough for introduction or connection of the gas and/or water conduits and for exhaust of the burned gases. Note also, that the pipe 42 can be omitted, with the threads which couple to the exhaust pipe 28 being formed in the divider 40, and with the disc 41 selectively perforated to provide communication between the combustion chamber and the volume within the support member 16. Alternative, more versatile support members are shown in FIGS. 10 and 13. Also a geophone may be used as the switch means 47, either as part of the source 10 or placed adjacent thereto in the formation.

The lower end of the barrel 12 is externally threaded as indicated by numerals 48, for receiving an internally threaded, cylindrical flange of the end plug 14. A circular plate 50 is integrally secured as by welding, within the end of the barrel l2, and is provided with a central aperture for receiving in welded, or otherwise sealed relation, the end of the air or water jetting pipe 32.

An annulus 52 is provided between the plate 50 and a facing internal surface of the end plug 14, which annulus 52 defines a manifold for delivering air or water from the jetting pipe 32 to the series of holes defining the jet nozzle means 20. The series of holes preferably, but not necessarily, are drilled through the end plug 14 tangent to the axis of the source, whereby introduction of air or water under pressure via the jetting pipe 32 and the annulus 52 provides a spiraling fluid jetting action from the jet nozzle means 20. The jetting action facilitates planting or burying the source, and provides a vacuum breaking means which assists in the retrieval of the gun from an unconsolidated formation or from a predrilled hole after the source has been fired. Further, air forced through the jet nozzle means 20 is useful in planting the source in a semi-consolidated medium such as desert sand, etc. Although the jetting nozzle means 20 is shown as an integral part of the source 10, it is to be understood that the means 20 can be omitted from the apparatus without detriment to the operation thereof.

A reversed barb type of thread is machined in the outer circumference of either end of the barrel 12 as indicated at 54, 56, which barbed threads extend, for example, a length of 4 inches along the outside of the barrel 12 at either end. The barbed threads 54, 56 provide means for locking and sealing the inflatable member 18 to either end of the barrel l2, utilizing the fastener means 22 of previous mention. The fastener means 22 may comprise selected hose clamps, which upon being tightened cause the material of the inflatable member 18 to be extruded into the threads to assure a watertight locking effect. An alternative means for locking the inflatable member 18 to the barrel is shown in FIGS. l0, 12, 13, 16, 18, 19.

As may be seen from FIGS. 1 and 2 the barrel 12 is provided with a spaced series of openings or slots 58, through which expanding gases of the combustion process are allowed to pass to provide the abrupt expansion of the inflatable member 18 in accordance with the invention. The slots 58 are preferably elongated in shape, are cut generally parallel to the axis of the barrel 12, and are evenly spaced about the circumference of the barrel. The widths and lengths of the slots 58 are commensurate with the spacing and widths of circumferentially disposed bands of ports 60 drilled in the diffuser 24 (further described below), whereby upon assembly of the diffuser within the barrel 12, each series or ring of circumferentially disposed slots 58 are alternately disposed between the successive bands of ports 60 in the diffuser. This arrangement tends to baffle the explosion within the combustion chamber, resulting in a diffusion or deflection of the initial impact and the flames of the explosion. Thus, the inflatable member 18 is not subjected to the direct impact, velocity and/or flames of the explosion. Only the burned expanding gases reach the inflatable member 18 to provide the abrupt expansion thereof and failure due to rupture of the member or other premature deterioration is lessened.

As noted above, the diffuser 24 preferably is formed of a length of metal tubing of sufiicient wall thickness, e.g., 3/16 inch to withstand the impulse or explosive energy generated by the ignition of the fuel. Its length and diameter are proportional to the size of the seismic source desired. The diffuser 24 is sealed at the lower end via a plate 61 (specifically if the jet nozzle action is employed), and is rigidly secured within the barrel 12 with the cylindrical annulus 62 therebetween of the order of 1% inch, as previously described. The size and the width of each band of ports 60 are chosen commensurate with the size of the chamber. That is, by way of example, the total combined cross sectional area of the ports 60 is preferably of the order of from 3 to times the inside cross sectional area of the diffuser 24. Each band of ports 60 is spaced apart along the length of the diffuser chamber, thereby providing solid, undrilled portions 64 in axial register with respective bands of slots 58 of the concentric barrel 12. Thus, as noted above the alternate arrangement of bands of ports 60 in the diffuser 24 and slots 58 in the barrel 12 provide a baffling efiect, whereby the initial impulse of explosion is deflected to allow the fuel to burn within the diffuser 24 while the gases inflate the inflatable member 18.

As shown in phantom line and indicated by numeral 18' in FIG. 1, the inflatable member 18, upon initiation of the explosion, is abruptly inflated to a diameter of the order of three to six times its diameter in the collapsed state, dependent upon the volume of the gas charge. The inflatable member 18 is formed preferably of a tough, resilient rubber material, with an inside diameter and length corresponding to the dimensions of the barrel 12 to which it is secured. Note that an alternative length is shown in FIG. 18. The material forming the inflatable member 18 has a strength necessary to withstand prolonged temperatures of the order of, for example, 400 to 1,000 F. The wall thickness and material are selected to withstand of the order of 200 PSI or more internally, with a minimum elongation of, for example, 600 percent and a capability of reaching 300 percent elongation in the order of, for example, 10 milliseconds. Although a specific combination of parameters are given herein, it is to be understood that various operating parameters are possible depending upon the application size, and desired seismic signal of the source.

The jet nozzle means 50 is used, and air or water is pumped into pipe 32, generally during the planting" or the retrieval operations of the source, and not during the actual operation of the source when generating seismic pulses. Thus, when the source 10 is forced into a soft unconsolidated formation, (marshlands) or in desert sands, the jetting action is used to help wash material from in front of the source to facilitate its entry. During the retrieval process, the jetting action may be used to break the vacuum which exists when the seismic source 10 is withdrawn from the formation, particularly in marshlands.

The combustible fuel provided via the gas fill and ignition tube 30 is generally an oxygen-propane mixture, which is injected through the diffuser 24 via a remote mixture-igniter apparatus generally disposed at the surface of the earth. By way of example, mixture-igniter apparatus of particular application with the invention is sold by Geospace Corporation under the trademark FLEX-O-FIRE. The apparatus, indicated at 31 of FIG. 1, is formed of a series of pressure regulators, a timer, gas mixture ratio nozzles, a 12 volt coil, a spark plug, and various solenoid valves. The loading pressure, the degree of loading, and the ratio of the combustible mixture is regulated at the surface via the apparatus (the pressure feedback means 33 of FIG. 1) which controls the fill pressure, and thus the energy which is generated upon ignition of the fuel within the combustion chamber of the source. Pre-ignition is provided at the surface and is directed via the fill and ignition tube 30 to the combustion chamber of the source, wherein ignition of the gas charge is effected.

Other mixture-igniter apparatus is available whereby the fuel mixture can be made at the surface and injected via the tube 30. Furthermore, the seismic source 10 of the invention can include mixing chambers intimate with the combustion chamber, in a manner known in the art, whereby oxygen and gas is separately introduced to the source, mixed utilizing gas mixture ratio nozzles and chamber, and then ignited via a spark plug secured within the diffuser 24 or barrel 12. Thus, various means of introducing the fuel into the source 10 and igniting same are possible within the spirit of the invention.

After ignition of the combustible fuel within the seismic source 10 and upon generation of the associated seismic pulse, the burned gases are exhausted from the source combustion chamber, preferably to the surface, via the exhaust valve means 26 and exhaust pipe 28. Prior to firing, the exhaust valve means 26 confines the fuel mixture within the diffuser 24 and barrel l2, and opens only after a selected pressure is exerted on the valve. Thus valve 26 provides a means for exhausting the burned gases at a selected operating pressure; that is, the valve 26 can be adjusted to vary the pressure opening point thereof. To this end, two different embodiments of the exhaust valve means 26 are shown in FIGS. 2 and 6-8.

Referring to FIG. 2, the exhaust valve means 26 includes a valve body 66 preferably of stainless steel and of sufficient wall thickness to retain and direct the burned gases from the diffuser 24 to the exhaust pipe 28. The valve body 66 is threadably secured to a valve seat 68 which, in turn, is threadably secured by means of threads 44 to the threaded pipe 42 connected to the bulkhead divider 40. The other end of the valve body 66 is coupled to the exhaust pipe 28 via a reducer coupling 70. The valve seat 68 has valve seat surfaces 72 formed in the inner circumference of either end thereof, whereby the valve seat 68 may be reversed to provide a second valve seat surface 72. A feather valve 74 is provided with a hemispherical sealing disc 76 which provides a seal against the facing seal seat surface 72. The yalve 74 has an axial plurality of fins 79 (FIG. 7) defining a valve guide 78, formed by machinin g a series of axially disposed grooves 80 about the circumference thereof. The total cross sectional area removed by the grooves 80 is, for example, approximately three times the cross sectional area of the valve seat 68 opening. The proportion varies commensurate with the size of the source. The valve seat surface 72 is ground or lapped to the exact radius of the sealing disc 76 to provide optimum sealing. A baffle 82 such as a metal plate may be provided in the region of the valve set 68 to prevent the direct exposure of the valve sealing disc 76 to the flame during the ignition of the fuel. The inside diameter of the valve body 66 is slightly larger than the diameter of the valve guide 78, and the feather valve 74 is thus reciprocally translatable within the valve body 66. A valve spring 84 is disposed within the valve body 66 between the feather valve 74 and a washer 86 and snap ring 88. The degree of pressure and thus the selected opening point of the exhaust valve means 26, is varied by selecting one of a series of snap ring grooves 90 machined in the inside diameter of the valve body 66, thereby decreasing or increasing the force exerted by the spring 84 against the feather valve 74.

A more sophisticated embodiment of the exhaust valve means 26 is shown in FIGS. 6-8 wherein, besides the features described above with reference to FIG. 2, there is included pneumatic cushion control means 92 for regulating the closing time of the exhaust valve means 26 after it has opened. After the ignition process within the seismic source 10, the exhaust valve means 26 opens due to the pressure generated within the combustion chamber, caused in part by the collapse of the inflatable member 18. The pneumatic cushion control means 92 provides means for adjusting the closing speed of the feather valve 74, to thereby allow an optimum exhausting of burned gases from within the source 10. Note that similar elements of the exhaust valve means of FIGS. 2 and 6 are similarly numbered.

Referring to FIGS. 6-8, the pneumatic cushion control means 92 is generally disposed within the valve spring 84 of FIG. 2, and includes an air cushion cylinder 94 mounted within the exhaust valve body 66 by means of, for example, four mounting lugs 96 integrally formed on the cylinder 94 and extending radially outward therefrom to secure between the snap ring 88 and another snap ring 98. A piston 100, including a series of piston rings 101 disposed about the circumference thereof, is slidably disposed within the cylinder 94 for axial translation therein. The piston is coupled to the feather valve 74 by means of a piston rod 102 which is secured to the valve guide 78 via a wrist pin 104. One end of the rod 102 is machined to a smaller diameter, which end is sealably disposed within the piston 100, and is free to move a selected small axial distance therein. O-ring seals 106 and 108 are provided between the rod 102, and an end flange of the air cushion cylinder 94 and the piston 100, respectively.

Check valve apertures 110 are provided along the axial length of the piston 100. A check valve disc 112 having a diameter large enough to cover thecheck valve apertures 110 in the piston 100, is secured to the smaller diameter end of the piston rod 102 by means of a retaining nut 114 threadably secured thereto. Thus, the check valve apertures 110 are closed at such time as the check valve disc 1 12 is pressed against the facing end of the piston 100. An air bleed jet 116 is disposed in the wall of the air cushion cylinder 94 between the piston 100 and the sealed end of the cylinder.

In operation, when the exhaust valve means 26 opens after ignition of the fuel mixture, feather valve 74 and the piston rod 102 move towards the exhaust pipe 28, opening the check valve apertures 1 10. The piston 100 moves a distance equal to the distance of the stroke of the feather valve 74. Air passes through the check valve apertures 110 into a cavity 118 between the piston 100 and the sealed flanged end of the air cushion cylinder 94. At this time the feather valve 74 is open, allowing the gases to be exhausted through the exhaust valve means 26 into exhaust pipe 28. Immediately thereafter as the feather valve 74 begins to close due to the compression of spring 84, the retaining nut 114 on the piston rod 102 moves the check valve disc 1 12 toward the piston 100, thereby closing the check valve apertures 110, trapping the air within the cavity 118. The air which is compressed within cavity 118 is then vented at an adjustable rate by means of the air bleed jet 1 16, allowing piston 100 to travel axially at selectable speed within the cylinder 94 to close the feather valve 74. The bleed jet 1 16 is interchangeable, whereby a different size orifice can accordingly be installed. The spring 84 force versus the bleed rate of air through the air bleed jet 116, determines the rate of closure of the exhaust valve means 26, i.e., the feather valve 74. Thus, a faster or slower closing rate can be provided for the feather valve 74 by changing the air bleed jet 116 to a larger or smaller orifice size, respectively.

Applications for the seismic source of the invention may arise wherein it is desirable to limit the maximum expansion of the inflatable member 18. Accordingly, as illustrated in FIG. 9, an expansion retainer net 122 may be disposed about the inflatable member 18. The net 122 is fabricated of, for example, A inch diameter glass woven, pre-stressed marine cord or flexible steel cable. It is woven into a net having, for example, 1 inch square openings 124 and is secured at each overlapping point by means of pressed metal clips 126. The expanded shape of the net 122 describes an elongated ellipse, wherein the ends of net 122 are disposed about the inflatable member 18 in the region of the clamping area. The ends are secured about the clamped portion of the inflatable member 18 by means of split clamps 128. Thus, the entire length of the inflatable member 18 is surrounded by the net 122. The maximum diameter of the net upon expansion is selected commensurate with the desired maximum diameter of the inflatable member 18. Upon ignition of the combustible fuels within the diffuser chamber 24, the inflatable member 18 thus is confined by the net 122 to a maximum selected diameter. The seismic source may be utilized, for example, in marine work at relatively shallow depths under water, or in air, etc, with a decreased likelihood of blowing out the inflatable member 18. When the inflatable member 18 collapses, the expansion retainer net 122 likewise collapses about the barrel 12.

A further embodiment of the present invention is shown in FIG. 9, wherein the elements consisting of the barrel 12, the diffuser 24 and their combined function, are performed by a single, thick walled, perforated cylinder, herein indicated as barrel 130. Thus, the embodiment of FIG. 9 is, in essence, a simplification of that of FIG. 2. Barrel 130 is provided with a series of bands of slots, or ports 132, which provide the baffling or diffusing effect to prevent rupture of the surrounding inflatable member 18. Thus, the amount of area removed from the barrel 130 by means of the slots or ports 132, by way of example only, is of the order of three to ID times the cross sectional area of the inside of barrel 130.

Referring now to FIG. 10, there is shown in greater detail an alternative embodiment 134 employing only a barrel 136 (with no diffuser tube), and an alternative configuration of perforations, threaded support member, etc. To this end, an inflatable member 138 is disposed about the barrel 136 as previously described. However, the member 138 is secured by means of respective pairs of grooves 140, 142 machined in the outer circumference of either end of barrel 136. Fastener means such as pairs of hose clamps 144, 146 are disposed about the inflatable member 138 in axial register with respective grooves 140, 142, whereby tightening the clamps extrudes the rubber material into the grooves to secure the member 138 thereto in sealed relation.

An end plug 148 is threadably secured to the end of the barrel 136 by internal threads 150 in the latter and matching external threads 152 in a hub 154 of the end plug. Seal means is provided in the form of an O-ring 156.

A modified support member 158, analogous to member 16 of previous description, is threadably secured to the opposite end of the barrel 136 with the same matching thread system which is used with the end plug 148. That is, the internal circumference of the barrel is threaded as at 160, and a hub 162 of an apertured support disc 164, has matching external threads 166 therein. As may be seen the threads 150 and 160 are the same type and have the same diameter, and accordingly, either end of the barrel 136 can threadably receive either the end plug 148 or the support member 158. Seal means (O-ring 168) is provided and also has the same configuration as seal means 156. The support member 158 further includes a support cylinder 170 12 welded to the circular plate 164 and a mounting bulkhead or divider 172 analogous to divider 40 of FIG. 2. The divider 172 has a threaded bore 174 for receiving the exhaust valve means 26 (of FIGS. 2 and 6), and a bore 176 for receiving a demountable gas fill and ignition tube portion 178.

Referring to both FIGS. 10 and 11, the barrel 136 is provided with a spaced plurality of perforations 180 which replace the bands of slots or ports 58 and 132 of FIGS. 2 and 9 respectively. Rows of the perforations are shown herein circumferentially spaced about the barrel in selected arrangement, but any of various arrangements, spacings and sizes may be utilized. The perforations 180 are modified by countersinking or otherwise forming a chamber as indicated at 182 to provide perforations which function as a venturi; i.e., as gases pass from the narrower perforation diameter into the countersunk region 182 of each perforation, the velocity of the gas decreases, thereby lessening the jet action of the gas against the inflatable member 138. An annular space may be provided between the barrel 136 and the inflatable member 138 to accent this affect further.

It is to be understood, that the countersunk perforation configuration may also be employed in FIGS. 1 and 2, with respect to either the barrel 12 or preferably the diffuser 24 thereof. That is, the type, arrangement etc, of the openings in either the barrel 12 or the diffuser 24 may be replaced by the countersunk perforations 180 of FIG. 10.

Referring to FIG. 12, there is shown an adapter 184 which is employed to couple one or more barrels 136 (FIG. 10) together, to define a single composite source using a plurality of sources 134. The unitary configuration is made possible due to the similar thread assemblies employed at either end of the barrel 136 described supra. The adapter includes a central divider 186 which may be solid or may have a central opening therethrough as shown. Symmetrical hubs 188, 190 are coaxially secured to the central divider 186 and likewise are either solid or hollow (as shown). External threads 192, 194 and seal means 196, 198 are provided on hubs 188, 190 respectively. FIG. 12 includes respective ends 200, 202 of two of the sources 134, 134" in position for assembly. In the embodiment shown, the adapter 184 is hollow to provide communication between the combustion chambers of the sources, whereby a gas fill and ignition tube 178 extends through the source 134" and adapter 184, to the mid point of the combustion chamber of source 134'. A second gas fill and ignition tube 178" for source 134" must be the same length as tube 178' to provide equal fill and particularly ignition times for the composite sources. Accordingly tube 178" extends to the adapter 184, is bent into a U-shape, and extends back to the mid-point of the source 178" combustion chamber. Thus simultaneous ignition to provide an additive effect in the signals generated by the two integral sources 134', 134", is assured. Exhaust may be efiected via the tubes 178 and 178" by means of a vacuum pump (not shown) such as described in FIG. 1.

Referring to FIGS. 13 and 14 there is shown a selfcooling embodiment 204 of the invention. The basic elements are analogous to those previously described, while various structural modifications are made to provide the source with an internal, self-contained, cooling means generally indicated by numeral 206. Accordingly, the barrels l2 and 136 of previous description are herein replaced by a spaced plurality of parallel tubes 208, preferably rectangular in cross section. The tubes 208 are axially arranged to provide spaces or slots analogous to the slots 58, or 132, or the perforations 180, of previous embodiments. An inflatable member 212 is disposed about the spaced plurality of tubes 208 in intimate contact with the flat surfaces thereof.

The tubes 208 are secured at opposite ends .to respective support blocks 214, 216 as by butting and welding them to the blocks, or by machining slots in the blocks receiving the ends and then welding etc. Passageways 218, 220 are drilled through the blocks 214, 216 respectively in register with the tubes 208 to provide communication from each tube to the volumes on the opposite sides of the blocks 214, 216. The external circumferences of the blocks are provided with pairs of grooves 222, 224 whereby the inflatable member 212 is sealably secured about the hollow tube assembly via respective pipe clamps 226, 228.

A lower cylindrical, heat radiator 230, formed, for example, of a heat conducting material such as aluminum, etc, and of selected length, is rigidly secured in sealed relation to the tube support block 214. As shown, the radiator 230 may be provided with radially extending fins 232 to provide additional surface area for optimizing the heat radiating property. The fins may extend axially rather than radially. The end of radiator 230 is internally threaded to receive the external threads of an end plug 148 as previously described.

An upper cylindrical heat radiator 236 of selected length is rigidly secured in sealed relation to the support block 216, and may be provided with radial fins 238. (The fins may be axially arranged). An inner cylinder 240 -is coaxially secured to the block 216 within the radiator 236 to provide an annulus 242 in communication with the respective ends of the series of radially spaced passageways 220. The free ends of the radiator 236 and the inner cylinder 240 are secured to a support member 158' analogous to the previously described support member 158 of FIG. 10. Thus the support member 158 includes the elements 164, 170 and 172 of FIG. 10. A gas fill and ignition tube portion 178 is also disposed through the mounting bulkhead or divider 172 and extends in sealed relation though the inner cylinder 240, the block 216 and to the mid-point of the combustion chamber formed by the plurality of tubes 208.

A cooling compound (indicated by numeral 244) having a high rate of heat dissipation, such as Dow Corning, DC-200, is disposed within the volume provided within the tubes 208, passageways 218 and 220, the radiator 230 and the annulus 242. In operation, heat produced by the gas explosion is conducted to the compound 244 via the tubes 208, whereupon the compound expands into the radiator 230 and the annulus 242 within radiator 236. The heat contained in the displaced compound is conducted to the surrounding formation via the radiators 230, 236 and fins 232, 238. Upon cooling, the compound circulates back into the tubes 208 and the cycle repeats.

Referring to FIG. 15, a modified drill bit" 246 isprovided in combination with an externally threaded hub 248, and seal means 250. The drill bit 246 includes an extended cone 252 about which one or more spiral flightings 254 are secured, and is used in place of the end plug (14, 148, 148') to assist in planting the source. The cone 252 can be hollow with jet ports formed therein, as shown in phantom and indicated by numeral 256, whereby the jetting action of previous mention, employing air or water, can be utilized to assist in the drilling process. In use, the source is attached to the push or drill tube (34 of FIG. 1) and is drilled and jetted into the formation.

FIGS. 16-18 show various modifications to the pre viously described inflatable members, the perforations, and/or the manner of securing the inflatable member to the barrel. Thus in FIG. 16, two configurations are shown for stiffening an inflatable member 258 in the region where it is secured to a barrel 260 via pairs of hose clamps 262. This region is where failure of the inflatable member frequently occurs. In one illustration, the wall thickness of the inflatable member 258 is progressively increased, as indicated at 264, to provide a stiffening and strengthening of the material prior to the clamped region. The thickened region not only provides additional strength, but provides resistance to undue flexing which would in turn cause rupture. In the other illustration, the end of the inflatable member 258 is strengthened by adding a second cylinder of inflatable material 266 around the conventional clamped region of the member 258. The second cylinder of material 266 extends axially beyond the slotted port (or perforated) region of the barrel 260 and provides added strength and stiffness to the member 258. The member 258 preferably is first clamped as at 268, and then the cylinder 266 is added.

FIG. 17 shows an alternative arrangement for the perforations of previous mention. The perforations 270 are smaller near the ends of a barrel or diffuser (indicated at 272), and larger towards the mid point thereof where initial ignition takes place. Thus the forces exerted against an inflatable member (not shown) disposed about 272 are greater at the center and less towards the (clamped) ends thereof, tending to reduce the rupture of the inflatable member at the ends. The perforations need not include the countersunk portions. The introduction and ignition of the gas provided by extending the gas fill and ignition tube 30 to the central region of the combustion chamber, also tends to reduce the undesirable forces in the clamping regions of the member.

FIG. 18 shows a barrel 274 wherein clamping of an inflatable member 275 is provided at a selected axial distance 276 away from the barrel's slotted region, i.e., from the combustion chamber region. The barrel 274 and inflatable member 275 are generally somewhat longer or the slotted region is made shorter, than utilized in the previous embodiments. Thus the initial detonation does not directly affect the previously mentioned normal failure points near the clamping region of the inflatable member.

Referring to FIG. 19, an alternative embodiment 278 of the invention is depicted, utilizing a boot-shaped inflatable member 280, closed at one end and coaxially disposed about a supporting barrel 282. The latter is selectively perforated as by slots or (as shown) by countersunk perforations 284, such as perforations 180 described in FIG. 10. The open end of the inflatable member 280 is secured as previously described, via slots and hose clamps or bands 286. Thus the inflatable member 280 is free at the lower end of the source 278, which allows axial as well as radial inflation without unduly flexing or otherwise straining the member 280 in the clamped region. The usual modifications; e.g., threaded connections; diffuser tube; slots and perforation shapes, arrangements; gas fill, ignition, and purging devices; etc, are applicable in the FIG. 19 embodiment.

We claim: 1. The gas seismic source for generating a seismic impulse under the surface of a surrounding medium, including an inflatable member expandable by means of ignition of a combustible fuel, comprising a combination of;

rigid elongated tube means of substantially constant outside diameter, having a selected size, spacing and arrangement of perforations therethrough, said tube means defining therein a single chamber defining a combustion chamber for directly receiving and igniting said combustible fuel, the size, spacing and arrangement of perforations providing a baffle arrangement for absorbing the initial flame and impact of the combustible fuel upon ignition;

the elongated tube means including means for closing one end thereof to further define one extremity of the combustion chamber, and threaded support means demountably coupled to the other end of the elongated tube means and having an outside diameter of the order of that of the inflatable member;

an inflatable member of substantially constant diameter disposed circumjacently about the elongated tube means to enclose the perforations therewithin, the member being sealably secured to and supported by the elongated tube means immediately about the single chamber defining the combustion chamber which directly receives the combustible fuel;

means for introducing said combustible fuel before ignition directly into the combustion chamber defined by the elongated tube means via the threaded support means, and for igniting the fuel at the point of introduction; and

valve means coupled to the threaded support means of the elongated tube means at the end thereof opposite the closed end, for providing initial exhausting of the combustion chamber upon expansion of the inflatable member prior to subsequent introduction of another charge of combustible fuel.

2. The seismic source of claim 1 wherein said elongated tube means includes an elongated barrel, said inflatable member being secured at either end to respective ends of the barrel to confine therein the single chamber defining the combustion chamber, said elongated barrel including the perforations of selected size, spacing and arrangement; and wherein the valve means for exhausting the combustion chamber further includes, feather valve means secured to the end of the source opposite that of the end plug means, said feather valve means including means for selectively varying the pressure at which the feather valve means opens.

3. The seismic source of claim 2, wherein the inflatable member includes resilient reinforcing means integral with the ends thereof to stiffen and strengthen a selected langth of the end portions thereof.

4. The seismic source of claim 2 wherein the elongated tube means includes a circularly spaced plurality of axially extending hollow tubes defining the single chamber forming the combustion chamber;

said perforations being defined by the spacing between tubes;

said inflatable member being disposed to confine the hollow tubes in contact therewith; at least one internally confined heat radiating means of selected volume and of an outside diameter substantially equal to the diameter of the inflatable member secured at one end of the plurality of hollow tubes with the volume thereof in communication with only the passageways of the hollow tubes;

and an internally confined heat dissipating fluid disposed within the hollow tubes and in the volume of the heat radiating means, and not in contact with the surrounding medium, to radiate to the surrounding medium upon expansion thereof heat received thereby from the inflatable member via the hollow tubes due to the fuel combustion.

5. The seismic source of claim 2 further including at least two coaxially spaced elongated tube means coupled end-to-end;

adapter means defining the means for closing one end, and threaded at either end to receive respective ends of two of said elongated tube means to provide a composite seismic source formed of two separated single chambers forming two respective combustion chambers confined by respective inflatable members; and

separate means for introducing said combustible fuel before ignition directly into respective combustion chambers and for igniting the fuel within the combustion chambers at essentially the same moment.

6. The seismic source of claim 2 wherein said elongated tube means includes elongated barrel means of selected length and substantially constant diameter and closed at one end, said barrel means being selectively perforated along at least a portion of the length thereof starting at the closed end;

said inflatable member being closed at one end to define a boot open only at one end, said boot being disposed concentrically about and thus enclosing the closed end of the elongated barrel means and the perforations therein, said boot being sealably secured to the barrel means at the open end.

7. The seismic source of claim 2 wherein the means for introducing and igniting includes a combustible fuel line extending through the threaded support means to a central region of the combustion chamber, and combustible fuel sensing means coupled therewith to control the amount of fuel introduced to the combustion chamber; and further including purge means coupled to the combustion chamber via the threaded support means and adapted to remove substantially all of the burned gasses after collapse of the inflatable member.

8. The seismic source of claim 7 wherein the purge means includes a valve integral with the means for introducing and igniting, and vacuum pump means selectively coupled to the valve to draw the burned gases from the combustion chamber upon collapse of the inflatable member.

9. The seismic source of claim 7 wherein the purge means includes a valve integral with the means for introducing and igniting, and compressor pump means selectively coupled to the valve to provide air under pressure to the combustion chamber to force substantially all the burned gases through the exhaust valve means.

10. The seismic source of claim 2 wherein the perforations in the elongated tube means define venturi type holes having diverging outer portions thereof confronting the confining inflatable member, whereby the velocity of the forces passing through the holes is decreased.

11. The seismic source of claim 2 further including end plug means for providing said means for closing the tube means, the end plug means including means for providing fluid jet means at the end of the seismic source, and fluid conduit means for supplying fluid under pressure to said fluid jet means.

12. The seismic source of claim 11 wherein the end plug includes a coaxially extending cone, and helical flighting is secured about the cone to define a drill bit.

13. The seismic source of claim 2 further including diffuser tube means secured within the barrel means, the diffuser tube means having a selected array of perforations therein to remove a total amount of surface area of the order of from three to 10 times the inside cross sectional area of the difiuser chamber.

14. The seismic source of claim 13 wherein the diffuser tube means array of perforations are alternately 18 disposed relative to succeeding unperforated portions thereof;

the perforations in the barrel means being alternately disposed with unperforated portions thereof, with the perforations in the barrel means being radially disposed in register with the unperforated portions of the diffuser tube and vice versa.

15. The seismic source of claim 13 wherein the diffuser tube means array of perforations define venturi type holes of selected size and spacing, having diverging outer portions thereof confronting the surrounding barrel means.

16. The seismic source of claim 2 wherein the exhaust valve means further includes air cushioning means for delaying the closure of the valve means a pre-selected time duration after ignition while exhausting the burned gases from the combustion chamber.

17. The seismic source of claim 2 further including time break switch means secured thereto to provide an electrical signal indicative of the time of ignition of the seismic source and thus of the generation of the seismic signal.

18. The seismic source of claim 2 further including generally elliptical collapsable net means disposed about the inflatable member and secured at either end to the elongated barrel means, said net means being adapted to restrain further outward movement of the inflatable member past a selected diameter. 

1. The gas seismic source for generating a seismic impulse under the surface of a surrounding medium, including an inflatable member expandable by means of ignition of a combustible fuel, comprising a combination of; rigid elongated tube means of substantially constant outside diameter, having a selected size, spacing and arrangement of perforations therethrough, said tube means defining therein a single chamber defining a combustion chamber for directly receiving and igniting said combustible fuel, the size, spacing and arrangement of perforations providing a baffle arrangement for absorbing the initial flame and impact of the combustible fuel upon ignition; the elongated tube means including means for closing one end thereof to further define one extremity of the combustion chamber, and threaded support means demountably coupled to the other end of the elongated tube means and having an outside diameter of the order of that of the inflatable member; an inflatable member of substantially constant diameter disposed circumjacently about the elongated tube means to enclose the perforations therewithin, the member being sealably secured to and supported by the elongated tube means immediately about the single chamber defining the combustion chamber which directly receives the combustible fuel; means for introducing said combustible fuel before ignition directly into the combustion chamber defined by the elongated tube means via the threaded support means, and for igniting the fuel at the point of introduction; and valve means coupled to the threaded support means of the elongated tube means at the end thereof opposite the closed end, for providing initial exhausting of the combustion chamber upon expansion of the inflatable member prior to subsequent introduction of another charge of combustible fuel.
 2. The seismic source of claim 1 wherein said elongated tube means includes an elongated barrel, said inflatable member being secured at either end to respective ends of the barrel to confine therein the single chamber defining the combustion chamber, said elongated barrel including the perforations of selected size, spacing and arrangement; and wherein the valve means for exhausting the combustion chamber further includes, feather valve means secured to the end of the source opposite that of the end plug means, said feather valve means including means for selectively varying the pressure at which the feather valve means opens.
 3. The seismic source of claim 2, wherein the inflatable member includes resilient reinforcing means integral with the ends thereof to stiffen and strengthen a selected langth of the end portions thereof.
 4. The seismic source of claim 2 wherein the elongated tube means includes a circularly spaced plurality of axially extending hollow tubes defining the single chamber forming the combustion chamber; said perforations being defined by the spacing between tubes; said inflatable member being disposed to confine the hollow tubes in contact therewith; at least one internally confined heat radiating means of selected volume and of an outside diameter substantially equal to the diameter of the inflatable member secured at one end of the plurality of hollow tubes with the volume thereof in communication with only the passageways of the hollow tubes; and an internally confined heat dissipating fluid disposed within the hollow tubes and in the volume of the heat radiating means, and not in contact with the surrounding medium, to radiate to the surrounding medium upon expansion thereof heat received thereby from the inflatable member via the hollow tubes due to the fuel combustion.
 5. The seismic source of claim 2 further including at least two coaxially spaced elongated tube means coupled end-to-end; adapter means defining the means for closing one end, and threaded at either end to receive respective ends of two of said elongated tube means to provide a composite seismic source formed of two separated single chambers forming two respective combustion chambers confined by respective inflatable members; and separate means for introducing said combustible fuel before ignition directly into respective combustion chambers and for igniting the fuel within the combustion chambers at essentially the same moment.
 6. The seismic source of claim 2 wherein said elongated tube means includes elongated barrel means of selected length and substantially constant diameter and closed at one end, said barrel means being selectively perforated along at least a portion of the length thereof starting at the closed end; said inflatable member being closed at one end to define a boot open only at one end, said boot being disposed concentrically about and thus enclosing the closed end of the elongated barrel means and the perforations therein, said boot being sealably secured to the barrel means at the open end.
 7. The seismic source of claim 2 wherein the means for introducing and igniting includes a combustible fuel line extending through the threaded support means to a central region of the combustion chamber, and combustible fuel sensing means coupled therewith to control the amount of fuel introduced to the combustion chamber; and further including purge means coupled to the combustion chamber via the threaded support means and adapted to remove substantially all of the burned gasses after collapse of the inflatable member.
 8. The seismic source of claim 7 wherein the purge means includes a valve integral with the means for introducinG and igniting, and vacuum pump means selectively coupled to the valve to draw the burned gases from the combustion chamber upon collapse of the inflatable member.
 9. The seismic source of claim 7 wherein the purge means includes a valve integral with the means for introducing and igniting, and compressor pump means selectively coupled to the valve to provide air under pressure to the combustion chamber to force substantially all the burned gases through the exhaust valve means.
 10. The seismic source of claim 2 wherein the perforations in the elongated tube means define venturi type holes having diverging outer portions thereof confronting the confining inflatable member, whereby the velocity of the forces passing through the holes is decreased.
 11. The seismic source of claim 2 further including end plug means for providing said means for closing the tube means, the end plug means including means for providing fluid jet means at the end of the seismic source, and fluid conduit means for supplying fluid under pressure to said fluid jet means.
 12. The seismic source of claim 11 wherein the end plug includes a coaxially extending cone, and helical flighting is secured about the cone to define a drill bit.
 13. The seismic source of claim 2 further including diffuser tube means secured within the barrel means, the diffuser tube means having a selected array of perforations therein to remove a total amount of surface area of the order of from three to 10 times the inside cross sectional area of the diffuser chamber.
 14. The seismic source of claim 13 wherein the diffuser tube means array of perforations are alternately disposed relative to succeeding unperforated portions thereof; the perforations in the barrel means being alternately disposed with unperforated portions thereof, with the perforations in the barrel means being radially disposed in register with the unperforated portions of the diffuser tube and vice versa.
 15. The seismic source of claim 13 wherein the diffuser tube means array of perforations define venturi type holes of selected size and spacing, having diverging outer portions thereof confronting the surrounding barrel means.
 16. The seismic source of claim 2 wherein the exhaust valve means further includes air cushioning means for delaying the closure of the valve means a pre-selected time duration after ignition while exhausting the burned gases from the combustion chamber.
 17. The seismic source of claim 2 further including time break switch means secured thereto to provide an electrical signal indicative of the time of ignition of the seismic source and thus of the generation of the seismic signal.
 18. The seismic source of claim 2 further including generally elliptical collapsable net means disposed about the inflatable member and secured at either end to the elongated barrel means, said net means being adapted to restrain further outward movement of the inflatable member past a selected diameter. 